A fourth UK case of a strain of mpox that is thought to spread more easily has been detected.
The UK Health Security Agency (UKHSA) said the overall risk to the population “remains low”.
The patient is a household contact of the first UK case, which was detected in London at the end of October.
The person is currently receiving specialist care at Guy’s and St Thomas’ NHS Foundation Trust in London.
According to UKHSA, they had been isolating since being identified as a contact of the first case, and so no further contact tracing is required.
Professor Susan Hopkins, chief medical adviser at UKHSA, said: “Mpox is very infectious in households with close contact and so it is not unexpected to see further cases within the same household.
“The overall risk to the UK population remains low.
“We are working with partners to make sure all contacts of the cases are identified and contacted to reduce the risk of further spread.”
The first UK case of Clade Ib mpox was contracted by a person who had been on holiday in Africa and travelled back to the UK on an overnight flight on October 21.
They developed flu-like symptoms more than 24 hours later and, on October 24, started to develop a rash which worsened in the following days.
Two more cases, also household contacts of the first patient, were announced on November 4, with the patients also getting specialist care at Guy’s and St Thomas’.
The World Health Organisation (WHO) said these are the first locally transmitted mpox Clade 1b cases in Europe, and the first outside of Africa since it declared a public health emergency of international concern because of the rapid spread of the strain in August.
Dr Hans Henri P Kluge, WHO’s regional director for Europe, said: “The overall risk to the general population in the UK and wider remains low, but local transmission of mpox clade Ib should be the impetus for health systems across our region to heighten their surveillance measures and be prepared for rapid contact tracing of suspected and confirmed cases.
“People who suspect they may be infected must also be encouraged to come forward for testing, care and preventing further transmission, free from stigma and discrimination.”
He added: “I commend the United Kingdom for its prompt action to detect and control this cluster, clear and transparent communication to ensure timely reporting, and data sharing.”
Mpox spreads between through direct contact with rash, skin lesions or scabs caused by the virus, including during sexual contact, kissing, cuddling or other skin-to-skin contact.
There is also a risk from contact with bodily fluids such as saliva or snot; contact with bedding or towels or clothing; and a possibility of spread through close and prolonged face-to-face contact such as talking, breathing, coughing, or sneezing.
Symptoms include skin rash with blisters, spots or ulcers that can appear anywhere on the body, fever, headache, backache and muscle aches.
A rash usually appears one to five days after a fever, headache and other symptoms.
Clade Ib mpox has been widely circulating in the Democratic Republic of Congo (DRC) in recent months and there have been cases reported in Burundi, Rwanda, Uganda, Kenya, Sweden, India and Germany.
A report from the World Health Organisation (WHO) and the Africa Centres for Disease Control and Prevention said there had been more than 40,000 mpox cases linked to almost 1,000 deaths in Africa as of the end of September 2024, with Clades Ia, Ib and II circulating in the region.